Methods for Detecting Defects in Inorganic-Coated Polymer Surfaces

ABSTRACT

Lipophilic fluorescent substances can be used to detect surface defects in materials having hydrophilic (e.g., inorganic) coatings. Use of the described methods makes surface defects appear fluorescent, while the remaining surfaces are not labeled. The disclosed methods are inexpensive, rapid, and easy alternatives to existing approaches.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/014,396, filed Dec. 17, 2007, the disclosure of which is incorporatedherein by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to methods for detecting surface defects in coatedsubstrates (e.g., inorganic-coated polymer surfaces) and, morespecifically, to the use of hydrophobic fluorescent materials to detectsurface defects.

DESCRIPTION OF RELATED ART

Polymers are commonly used materials because of their flexibility, lightweight, and low cost. Many polymer properties could be enhanced by theaddition of an inorganic coating on their surface. This inorganic filmcould serve as a gas diffusion barrier for various packagingapplications. The inorganic layer could also serve to protect theunderlying polymer and give the polymer higher strength. Unfortunately,inorganic layers are difficult to deposit on polymers because thedeposition of inorganic materials is usually performed at temperaturesabove the melting temperature of the polymer.

Alumina-coated polymer surfaces are widely used in industrial andconsumer products. Atomic layer deposition (“ALD”, sometimesalternatively referred to as chemical vapor deposition “CLD”) is used todeposit a thin nanometer layer of alumina or other inorganic or metallicmaterials onto a polymer surface. ALD coatings can be used to insulate,facilitate charge dissipation and functionalize the surface of MEMS(Micro-Electro-Mechanical Systems) devices. Polyimides are commonly usedas the polymer. Materials such as alumina-coated polyimides are used inthe semiconductor industry to prepare high vacuum, vapor resistantsealing packages for semiconductor wafers.

Due to inherent limitations and variability in atomic layer deposition,various defects such as non-coated areas, surface irregularities,cracks, or scratches can be introduced during large scale production.These defects can be introduced during the deposition of the inorganiclayer, or afterwards during further processing or handling.

Several quality control testing procedures exist, but tend to be costly,time consuming, and expensive. One example is a helium leakage test.This test measures the vapor transmission rate through the polymer as anindicator of the integrity of the inorganic coating. This test canindicate the presence of a defect, but does not allow detection of theexact location of the defect.

Other tests for water vapor permeation include gravimetric (loss ofwater or gain of water on P₂O₅), capacitive or resistive (using ahumidity sensor), spectroscopy, calcium degradation (either optical orchange in resistance), and radioactive (using tritium or ¹⁴CO).

A publication described a method for detecting under-film corrosionusing a hand-held UV lamp (D. E. Bryant and D. Greenfield, Progress inOrganic Coatings, 57(4): 416-420 (2006)). The chemical8-hydroxyquinoline-5-sulfonic acid hydrate was used to study corrosionof coated aluminum, and 9-anthyl-5-(2-nitrobenzoic acid) disulfide wasused with iron. Metals coated with various polymers were scored with ascalpel, allowing corrosion to occur.

Atomic force microscopy (“AFM”) was used to examine surface cracks on anindium tin oxide coated polycarbonate substrate that had been subjectedto cycles of bending (L Ke et al., Applied Physics A: Materials Science& Processing, 81(5): 969-974 (2005)). AFM showed that bending increasesthe roughness of the inorganic coating surface. Calcium degradation testshowed that surface cracks are perpendicular to the flexing direction,and that barrier performance deteriorated after bending. An organiclight emitting device (“OLED” or “organic LED”) fabricated on thesurface showed decreased electrical and optical performance due tomoisture and oxygen permeation.

An auto-optical inspection system (“AOI”) for detection of defects inOLEDs was described by D. B. Perng et al., Journal of Physics:Conference Series, 13: 353-356 (2005). The publication indicated thatOLED defects commonly include dark points, non-uniform luminescence,surface scratches, insufficient rubber widths, and lack of coloruniformity. The computer-controlled AOI is based on a lighting mechanismincluding a conducting fixture, a UV light, a coaxial LED light, and aback light.

Various U.S. patents have issued offering methods for detecting surfacedefects of materials.

U.S. Pat. No. 4,968,892 (issued Nov. 6, 1990) describes a testingapparatus for identifying surface defects in a workpiece. The piece istreated with a fluorescent substance that is trapped in flaws in thesurface. The apparatus includes a light source, lenses, and filter toscan the surface.

U.S. Pat. No. 5,723,976 (issued Mar. 3, 1998) describes a method fordetecting defects in encapsulated electronic components. The methodinvolves immersing the component in an aqueous florescent solution of awater-soluble fluorescent substance that fluoresces when moistened, butthat does not fluoresce when dry. The component is visualized in humidair, and then in dry air to detect fluorescence (when moist) and lack offluorescence (when dry) at a defect.

U.S. Pat. No. 5,965,446 (issued Oct. 12, 1999) suggests a method ofdetecting defects in surfaces. A solution of fluorescent molecules in avolatile organic solvent is prepared, and applied across the surfaceusing a slip of paper. The paper is used to uniformly distribute thesolution across the surface before the organic solvent evaporates.

U.S. Pat. No. 6,097,784 (issued Aug. 1, 2000) offers a method foramplifying defects connected to a top surface of a semiconductor device.A dye is applied to the top surface, and leeched into a developing gel.The gel develops defect indications that are more easily visualized thanthe defects themselves. The dye can be a fluorescent dye.

U.S. Pat. No. 6,427,544 (issued Aug. 6, 2002) suggests anenvironmentally friendly method for detecting defects in parts. Theparts are submerged in a mixture of a penetrant dye and supercriticalcarbon dioxide. The part is removed, and inspected for the presence ofdye in any defects. The dye can be a fluorescing penetrant dye that isvisualized with UV light.

U.S. Pat. No. 6,677,584 (issued Jan. 14, 2004) offers a manufacturingfluid containing a fluorescent dye. A component is either ground or cutin the presence of the manufacturing fluid, and the component issubsequently inspected for surface cracks or defects. The manufacturingfluid can be especially useful in processing of ceramic parts.

U.S. Pat. No. 6,916,221 (issued Jul. 12, 2005) describes an opticalmethod for determining defects in OLEDs. A digital image of the excitedOLED surface is obtained, and a computer or user inspects the image todetermine defects.

U.S. Pat. No. 6,943,902 (issued Sep. 13, 2005) describes a method ofdetermining layer thickness or respective amount of filling, layerthickness distribution, defect, accumulation or inhomogeneity within amaterial layer. The material is mixed with an agent that absorbsradiation before the layer is prepared. The layer is irradiated, and theemitted light is detected. In this method, the agent is permanentlyembedded throughout the layer.

While inorganic-coated polymers are widely used in industry, surfacedefects degrade, and potentially eliminate, the desirable properties ofthe materials. For example, a defect may allow water to penetrate thematerial, or may reduce the ability of the material to hold a vacuum.Thus, despite efforts made to date, simple, reliable methods to verifythe integrity of materials, or conversely, simple, reliable methods todetect surface defects of materials are still needed. Additionally,methods that provide detection of the location of the defects aredesirable.

SUMMARY OF THE INVENTION

Surface defects in materials having a polymer layer coated with ahydrophilic layer (e.g., a surface layer of an inorganic substance) canbe detected and localized using at least one lipophilic fluorescentsubstance. Contacting the material with the fluorescent substancerenders any surface defects fluorescent, while the remaining surfacelacking defects is not labeled.

In one aspect, a method is provided for identifying a defect in asurface. The method involves a) providing a substrate having ahydrophobic surface at least partially coated by a hydrophilic layer,wherein the hydrophilic layer has the defect therein; b) contacting thesubstrate with a lipophilic, fluorescent substance, for a sufficientamount of time for the substance to contact the defect; c) exciting thefluorescent substance with energy at an appropriate wavelength togenerate a detectable fluorescence response; and d) detecting thefluorescence response of the substance. The method can further includewashing the substrate after contacting the substrate with thelipophilic, fluorescent substance. The substrate can include a polymer.The hydrophilic layer can be or include an inorganic material (e.g., ametal oxide). The hydrophilic layer is typically less than 10 Å inthickness. The lipophilic, fluorescent substance can be a fluorescentcompound that includes a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacenemoiety. The lipophilic, fluorescent substance can further include alipophilic moiety or can include two or more lipophilic moieties. Forexample, the lipophilic moiety can be a hydrocarbon having 1-20 carbonatoms, such as an alkyl group having 1-20 carbon atoms or a phenyl orstyryl group. The lipophilic, fluorescent substance can be associatedwith a microparticle or a semiconductor nanocrystal.

In another aspect, a lipophilic, fluorescent substance is provided thatincludes a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene moiety and alipophilic moiety. The lipophilic moiety can be a hydrocarbon having1-20 carbon atoms, such as an alkyl group having 1-20 carbon atoms or aphenyl or styryl group. The lipophilic, fluorescent substance can beassociated with a microparticle.

In yet another aspect, a substrate is provided that includes anidentifiable defect. The substrate can include a hydrophobic surfacethat is at least partially coated by a hydrophilic layer (e.g., aninorganic material) in which there is a defect. A lipophilic,fluorescent substance can be in contact with the defect. Any lipophilic,fluorescent substance can be in contact with the defect, including, forexample, a substance that includes a4,4-difluoro-4-bora-3a,4a-diaza-s-indacene moiety and a lipophilicmoiety.

In yet another aspect, kits are provided including a lipophilic,fluorescent substance and, optionally, additional components forcarrying out the disclosed methods.

The compositions, kits, and methods provided herein offer numerousadvantageous over traditional approaches for visualizing surface defectsand provide an inexpensive, rapid, and relatively easy to usealternative to existing approaches.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an image demonstrating that lipophilic, fluorescent moleculesadhere selectively to scratches introduced in an ALD alumina coating.

FIG. 2 shows images of cracks in an ALD alumina coating rendered visibleby a lipophilic, fluorescent substance: (A) series of channel cracksgenerated at the specimen's interior after a 5% externally appliedstrain, (B) cracks at edge of specimen resulting from shearing duringsample preparation, (C) FESEM image demonstrating the true size of asingle shear crack.

FIG. 3 shows images of individual defects in/on an Al₂O₃ ALD filmrendered visible by a lipophilic fluorescent tag: (A) defect density andlocation revealed relative to a marker at low magnification via confocalmicroscopy; (B, C) details of size and morphology of defects at site #1and site #2 in (A) identified by high magnification FESEM.

DETAILED DESCRIPTION OF THE INVENTION

Before describing the present invention in detail, it is to beunderstood that this invention is not limited to specific compositionsor process steps. It should be noted that, as used in this specificationand the appended claims, the singular form “a”, “an” and “the” includeplural references unless the context clearly dictates otherwise. It alsoshould be noted that the term “about”, when used to describe a numericalvalue, shall encompass a range up to ±15% of that numerical value,unless the context clearly dictates otherwise. While compositions andmethods are described in terms of “comprising” various components orsteps (interpreted as meaning “including, but not limited to”), thecompositions and methods can also “consist essentially of” or “consistof” the various components and steps, such terminology should beinterpreted as defining essentially closed-member groups.

Compositions and Methods of Use

Methods are provided for the detection of defects in a material. Oneembodiment of the invention is directed towards methods for thedetection of surface defects in a material. The material can comprise,for example, a polymer layer coated with an inorganic layer. The methodcan comprise contacting the material with at least one lipophilicfluorescent substance to allow the substance to localize at the defect,and detecting the localized substance. The method can be used to detectvarious types of surface defects, including, without limitation,mechanical defects, such as cracks, pin holes, surface irregularities,scratches, uncoated areas, flaking, or any other type of defect that canarise during production or handling of the material. Also provided aremethods for detecting the presence of surface particles or contaminants(e.g., grease, oil, dust, fibers, and the like). The present methods canbe used for detecting defects that traverse the full thickness of asurface layer on a substrate. For example, a crack or pin hole in ahydrophilic coating that leaves a portion of an underlying hydrophobicsubstrate exposed can be detected using the subject lipophilicfluorescent substances. The disclosed fluorescent substances can labelsurface defects ranging in size from several to hundreds of nanometersto microns or larger. For example, defects can be identified having awidth or diameter (e.g., in the case of a pinhole defect) of about 500nm or less; or about 250 nm or less; or about 100 nm or less; or 50 nmor less.

The material can generally be any material. Examples of materialsinclude OLEDs (organic light-emitting diodes), thermal ground planes,solar panels, films and bags (such as those used the electronics, foodpackaging, or medical device industries), fiber optics, flexibledisplays, liquid crystal display (LCD) assemblies, flat panel displays,magnetic information storage media (MIS), Micro-Electro-MechanicalSystem (MEMS), and Ultra large-scale integration (ULSI) circuits.

The material can include a polymer or a combination of polymers. Thepolymer can be in the form of a surface layer. The polymer or polymerlayer can generally be any polymer. The polymer is preferablyhydrophobic. Examples of polymers include polystyrene, polyurethane,polyimide, epoxy, polyethersulfon (PES), polyethylene naphthalate (PEN),HSPEN (heat stabilized polyethylene naphthalate), KAPTON (a polyimidemembrane commercially available from DuPont), polyetheretherketone(PEEK), polysulfone (PSF), polyetherimide, polyethylene phthalate, andpolyethylene terephthalate (PET). The polymer can generally be in anythree-dimensional configuration. Examples of configurations includeplanar sheets, films, coatings, tubing, fibers, and beads.

The material (e.g., a substrate formed of a polymer) can further includeat least one layer of a coating. The coating can be a continuous coating(e.g., a film) or can cover only a portion of the substrate. The coatingcan include any type of material (e.g., a polymer or an inorganicmaterial), so long as it is less hydrophobic than the substratematerial. For example, the coating can be a hydrophilic material (e.g.,a hydrophilic polymer or an inorganic material). In certain embodiments,the coating is an inorganic layer. The inorganic layer can generally beany inorganic layer. The inorganic layer is preferably hydrophilic.Inorganic layers can be metal oxide layers. Inorganic layers can bemetal-anion solids such as ZnS, GaP, Ta₂O₃, Al₂O₃ (alumina), TiO₂, GeO₂,and VO_(x). The coating can range in thickness. For example, thecoatings can be less than about 1 micron; or less than about 500 nm; orless than about 100 nm; or less than about 50 nm. The coating can beapplied or deposited onto a substrate by any means known used in theart. In certain embodiments, an inorganic coating layer is applied byatomic layer deposition (ALD) to form a film on the substrate having athickness of 50 nm or less (e.g., about 25 nm).

The lipophilic fluorescent substance can generally be any lipophilicfluorescent substance. Examples of lipophilic fluorescent substancesinclude fluorescent dyes, fluorescent microspheres, and quantum dots(sometimes referred to as semiconductor nanocrystals). The fluorescentsubstance can generate fluorescence prior to application to the sampleor can generate fluorescence during use (e.g., upon contact with thesample). For example, lipophilic, fluorescent substances can appearnon-fluorescent or minimally fluorescent when dissolved in an aqueoussolution, such as water or a buffer. However, when in a hydrophobicenvironment (e.g., when in contact with a hydrophobic surface), certainlipophilic fluorescent substances (e.g., diaza-indacenes, squarenes andsome styryl dyes) can produce an intense fluorescence signal. The typeof lipophilic fluorescent substance used in the present methods can varydepending on, for example, the composition and configuration ofsubstrate and coating, the thickness of the coating, and the type andsize of defect. Lipophilic fluorescent substances are generally of asize that permits ready entry into nanometer-scale defects. Certainsubstances provided herein are relatively small molecules (e.g.,molecular weight of about 200-400). However, larger fluorescentsubstances with dimensions in the nanometer or micron range may bedesirable for detecting larger defects. Lipophilic fluorescentsubstances are typically hydrophobic compounds or substances that tendto be non-polar and are not considered water soluble. Liphophilicsubstances tend to dissolve in non-polar solvents, such as, methylenechloride, isopropanol, ethanol, hexane, and the like, and have noaffinity or a negligible affinity for hydrophilic surfaces. Thefluorescent substance itself may be lipophilic. Alternatively, thefluorescent substance includes a fluorescent moiety and a lipophilicmoiety (e.g., a lipophilic pendant group). Certain fluorescent moietiescan be lipophilic. In certain embodiments, the fluorescent moiety isrelatively less lipophilic than the lipophilic moiety. Certainfluorescent moieties can be hydrophilic. A fluorescent substance havinga fluorescent moiety that is relatively less hydrophobic than thependant moiety can be used when it is desired that the substance orientitself relative to the surface. For example, when deposited onto ahydrophobic surface, a lipophilic pendant group can adhere to thesurface (e.g., by hydrophobic interactions), while the relatively lesshydrophobic fluorescent moiety can present itself away from the surface.The lipophilic moiety can be bonded (e.g., covalently bonded) to afluorescent molecule and can further include a spacer that can distancethe lipophilic moiety from the fluorescent moiety. In certainembodiments, the fluorescent molecule can include more than one pendantgroup, where the pendant groups can be the same or different. Forexample, the compound can include 2 or 3 or 4 or more lipophilic groups,which can be the same or different. Lipophilic groups are typicallychosen so as not to interfere with the fluorescence properties of thefluorescent molecule. Any type of lipophilic or hydrophobic group can beused in the preparation of lipophilic, fluorescent substances and arewell known to those skilled in the art. A representative class oflipophilic moieties includes hydrocarbons. Hydrocarbons can be saturatedor unsaturated, linear, branched, or cyclic, and can include aliphatic,and/or aromatic moieties. Certain hydrocarbons include a conjugatedhydrocarbon chain. Exemplary lipophilic hydrocarbon moieties includealkyl groups having 1-20 carbon atoms. For example, the lipophilicmoiety can be a saturated alkyl group having 10 or less carbon atoms(e.g., 1 to 3; or 3 to 5; or 5 to 7; or 7 to 9; or 10), which can besubstituted or unsubstituted (e.g., methyl, ethyl, propyl, butyl, andthe like). Alternatively, the lipophilic moiety can be an unsaturatedhydrocarbon, which can be substituted or unsubstituted, or a conjugatedhydrocarbon with alternating single and double bonds. Other exemplarylipophilic moieties are or include an aromatic moiety, such as phenyl orstyryl. Other classes of lipophilic moieties include compounds thatcontain a heteroatom, such as N, S, O, or a halogen. Yet other classesof lipophilic substances include fatty acids, fatty sulfonic acids orfatty sulfates (such as sodium dodecyl sulfate). In certain embodiments,the fluorescent substance is substituted with 2 to 4 or more lipophilicpendant groups, which can be the same or different. For example afluorescent substance can be substituted with 2 or 3 or 4 alkyl groups,where each alkyl group has 1-20 carbon atoms (e.g., methyl, ethyl,propyl, butyl, and the like). In other embodiments, the fluorescentsubstance is substituted with more than one type of lipophilic group.For example, a fluorescent substance can be substituted with acombination of moieties, such as, for example hydrocarbon moieties(e.g., linear or branched alkyl, phenyl, styryl, or the like).

Examples of lipophilic fluorescent substances include fluorescent dyes,fluorescent microspheres or microparticles, and quantum dots (sometimesreferred to as semiconductor nanocrystals). Any type of fluorescent dyemay be used in the practice of the described methods. In certainembodiments, the fluorescent dye can absorb or emit radiation in thevisible range of the electromagnetic spectrum. Alternatively, thefluorescent dye can absorb or emit radiation in the near IR region ofthe spectrum. Near IR dyes can be effectively used to visualize defectsin substrates that generate background fluorescence. Many fluorescentcompounds tend to lose fluorescence emission intensity (referred to as“photobleaching”) upon sustained illumination (e.g., from seconds tolonger exposure times). Photobleaching arises for various reasons,including, for example, irreversible modification of the dye structure.Lipophilic, fluorescent substances are provided that resistphotobleaching and are, therefore, well-suited for use in detection andcharacterization of defects according to the methods provided herein.

Loss of fluorescence emission intensity also can occur when afluorescent substance is present in a high concentration oragglomerates. Thus, it is generally desired to use a lipophilicfluorescent compound in the practice of the disclosed methods thatexhibits minimal or no loss in fluorescence emission intensity whenpresent at a high concentration (e.g., when localized in or on adefect), or exhibits a loss in intensity or at a rate that is slowerthan the time scale of the detection period (such that the loss inintensity does not affect the measurement). Provided herein arefluorescent substances that are sufficiently lipophilic to adhere tohydrophobic substrates (e.g., polymers) and yet maintain theirfluorescence emission intensity when deposited in or on a surfacedefect. In contrast to many fluorescent compounds, it has been foundthat certain lipophilic, fluorescent compounds provided herein (e.g.,BODIPY dyes) actually exhibit an increase in fluorescence signalintensity when present in high concentration. Particular dyes, whereinthe dye is hydrophobic, provided herein (e.g., BODIPY) maintain orincrease fluorescence signal intensity when used to detect surfacedefects. This unique attribute is particularly advantageous in theimaging of micron or nanometer sized defects containing minutequantities of the fluorescent material. Although not necessary for thepractice of the described methods, particular lipophilic, fluorescentcompounds provided herein also can exhibit a shift in emissionwavelength (e.g., red-shift) when localized within a defect. Compoundsthat exhibit a spectral shift towards longer wavelengths can be used,for example, to visualize defects in substrates that produce backgroundfluorescence.

One representative class of hydrophobic fluorescent dyes that issuitable for detecting surface defects includes compounds having a borondipyrromethene (abbreviated as BODIPY) core structure (e.g., compoundshaving a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene core). BODIPY-basedcompounds can be substituted with one or more lipophilic pendant groups,as described herein. Particular examples of BODIPY-based fluorescentcompounds that can be utilized in the described methods include thosesubstituted with, for example, a hydrocarbon, such as methyl, propyl,phenyl, or styryl. For example, representative BODIPY compounds include,1,3,5,7,8-pentamethyl BODIPY and 1,3-di-n-propyl BODIPY.

Other examples of BODIPY-based fluorescent compounds that can beutilized in the described methods include4,4-difluoro-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indacene;4,4-difluoro-1,3-dimethyl-5,7-diphenyl-4-bora-3a,4a-diaza-s-indacene;4,4-difluoro-1,3,5,7-tetraphenyl-4-bora-3a,4a,8-triaza-s-indacene;4,4-difluoro-1,3-diphenyl-5-(2-pyrrolyl)-4-bora-3 a,4a-diaza-s-indacene;4,4-difluoro-1,3-dipropyl-4-bora-3a,4a-diaza-s-indacene;4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3 a,4a-diaza-s-indacene,4,4-difluoro-1,3-diphenyl-5,7-dipropyl-4-bora-3a,4a-diaza-s-indacene;4,4-difluoro-1-phenyl-3-(4-methoxyphenyl)-5-(2-pyrrolyl)-4-bora-3a,4a-diaza-s-indacene;difluoro(1-((3-(4-methoxyphenyl)-2H-isoindol-1-yl)methylene)-3-(4-methoxyphenyl)-1H-isoindolato-N¹,N²)boron;difluoro(5-methoxy-1-((5-methoxy-3-(4-methoxyphenyl)-2H-isoindol-1-yl)methylene)-3-(4-methoxyphenyl)-1H-isoindolato-N¹,N²)boron;4,4-difluoro-2-ethyl-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indacene;4,4-difluoro-1,3-dimethyl-5-styryl-4-bora-3a,4a-diaza-s-indacene;4,4-difluoro-3,5-di(4-methoxyphenyl)-4-bora-3a,4a-diaza-s-indacene;3-decyl-4,4-difluoro-5-styryl-4-bora-3 a,4a-diaza-s-indacene;4,4-difluoro-1,3-dimethyl-5-(4-methoxyphenyl)-4-bora-3a,4a-diaza-s-indacene;4,4-difluoro-1,3-dimethyl-5-(2-thienyl)-4-bora-3 a,4a-diaza-s-indacene;difluoro(1-((3-(2-(5-hexyl)thienyl)-2H-isoindol-1-yl)methylene)-3-(2-(5-hexyl)thienyl)-1H-isoindolato-N¹,N²)boron;4,4-difluoro-1,3,5,7-tetraphenyl-4-bora-3 a,4a-diaza-s-indacene;4,4-difluoro-1,3-dimethyl-5-(2-(5-methoxycarbonyl-4-methyl-2-oxazolyl)ethenyl)-4-bora-3 a,4a-diaza-sindacene; anddifluoro(5-methoxy-1-((5-methoxy-3-(2-(5-(4-methoxyphenyl))thienyl)-2H-isoindol-1-yl)methylene)-3(24544-methoxyphenyl))thienyl)-1H-isoindolato-N¹,N²)boron.

Yet other examples of hydrophobic fluorescent dyes that can be used inthe practice of the described methods include p-aminophenylphosphorylcholine, naphthalenes, anthracenes, phenanthrenes, indoles,carbazoles, stilbenes, benzimidazoles, benzoxazoles, benzothiazoles,quinolines, benzoxanthrones, oxazoles, isoxazoles, oxadiazoles,benzofurans, pyrenes, perylenes, coronenes, coumarins, carbostyryls,bimanes, acridines, polyphenylenes such as terphenyl, alkenyl andpolyalkenyl dyes (including 1,6-diphenyl-1,3,5-hexatriene and1,1,4,4-tetraphenyl-1,3-butadiene).

Other long wavelength dyes such as luminescent phenoxazones, oxazinesand pyronines (including nile red); porphines, porphyrins,phthallocyanines and their metallated complexes, including complexeswith rare earth ions such Eu³⁺ and Tb³⁺; xanthenes (includingfluoresceins and rhodamines); cyanine, carbocyanines and merocyanines(including styryl dyes; hydrocarbon derivatives such as rubrenes andazulenes; are suitable provided that they are either electricallyneutral; or their ionic charges are balanced by lipophilic counterionsthat include but are not limited to lipophilic ammonium salts (such ashexadecyltrimethylammonium or benzyltrimethylammonium), fatty acids,fatty sulfonic acids or fatty sulfates (such as sodium dodecyl sulfate),detergents such as anionic or cationic derivatives of cholic acids,tetraarylphosphonium or tetraarylboride; or they contain a suitablefunctional group (as described above) for copolymerization.

The fluorescent lipophilic substance may be contained within or on amicroparticle (e.g., a spherical particle). Microparticles include thosesized so as to be able to readily enter a defect (e.g., a crack orpinhole) in a surface. In certain embodiments, the fluorescentlipophilic substance is contained within or on a microparticle havinglow surface charge (e.g., particles with lipophilic surfaces).Microparticles can generally have any shape or size. For example,microparticles can be sized to have a dimension along the longest axisthat can be about 5 nm to about 20 μm. Certain microparticles can bespherical (referred to as microspheres). The spherical microspheres cangenerally have any diameter. Generally, the diameter (or length acrossthe longest dimension, in the case of non-spherical particles) can beabout 5 nm to about 20 μm. Presently preferred diameters are about 10 μmto about 100 nm. Specific examples of diameters include about 5 nm,about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11nm, about 12 nm, about 13 nm, about 14 nm, about 16 nm, about 17 nm,about 18 nm, about 19 nm, about 20 nm, about 21 nm, about 22 nm, about23 nm, about 24 nm, about 25 nm, about 26 nm, about 27 nm, about 28 nm,about 29 nm, about 30 nm, about 40 nm, about 50 nm, about 60 nm, about70 nm, about 80 nm, about 90 nm, about 100 nm, about 200 nm, about 300nm, about 400 nm, about 500 nm, about 600 nm, about 700 nm, about 800nm, about 900 nm, about 1 μm, about 2 μm, about 3 μm, about 4 μm, about5 μm, about 6 μm, about 10 μm, about 20 μm, about 30 μm, about 1 μm,about 2 μm, about 3 μm, about 4 μm, about 10 μm, about 20 μm and rangesbetween any two of these values. In certain embodiments, particles ofless than 1 micron; or less than 500 nm; or less than 100 nm aresuitable for use in methods to visualize micron to nanometer-sizeddefects.

The spherical microspheres can be prepared from generally any material.It is presently preferred that the spherical standards are prepared froma polymer material. Example polymer materials include polymers andcopolymers of styrenes and divinyl benzenes; an acrylate or methacrylateester; an acrylic acid or methacrylic acid; an acrylamide ormethacrylamino; an acrylonitrile or methacrylonitrile; vinyl andvinylidene halides, esters and ethers; alkenes, including ethylene,propylene, butadiene and isoprene; epoxides and urethanes.

The spherical microspheres can be stained with at least one fluorescentcompound, such as the dyes described above. The one or more fluorescentdyes in the spherical microspheres can be selected to match theexcitation source (e.g., a laser such as an argon-ion laser, akrypton-argon laser, or a helium-neon laser, a LED, UV lamp, etc.),and/or an optical filter commonly used in scanner, fluorescencemicroscopes or confocal laser-scanning microscopes. For example, certainmicrospheres for use according to the described methods have diametersof about 10 nm or less and low surface charge loaded with a fluorescentdye that emits fluorescence in the green region of the electromagneticspectrum.

The lipophilic, fluorescent substance can be a quantum dot (alsoreferred to as a “semiconductor nanocrystal” or “nanocrystal”). Quantumdots are nanometer-scale atom clusters formed of a core (typically zincsulfide), a semiconductor shell, and coating. A lipophilic moiety can beattached to the polymer coating or directly to the semiconductor shellto create nanocrystals that meet specific defect detection requirementsand to minimize non-specific attachment of the quantum dot to thesurface. The surface of the quantum dots can be relatively hydrophobic,and can interact with un-coated (defect of ALD deposition) polymer(e.g., membrane) surfaces by hydrophobic interactions and lead to defectdetection. Typically, quantum dots can be excited with shorterwavelength excitation sources such as UV or violet laser and can emit atwavelengths in the visible region to the near infrared region of theelectromagnetic spectrum (e.g., at about 500 to about 800 nm). Quantumdots can produce a bright fluorescence signal and are typically morephotostable and less susceptible to bleaching than traditional organicfluorophores, even under high power excitation over extended periods oftime (e.g., up to several hours). Further, quantum dots do not generallyexhibit a marked reduction in fluorescence emission intensity whenaccumulated at higher concentration. As was discussed with reference tocertain classes of lipophilic fluorescent dyes, quantum dots thatmaintain fluorescence emission intensity during use are generallydesirable for use in visualization of surface defects. Quantum dots cangenerally be any color quantum dot. Examples of currently commerciallyavailable quantum dots suitable for use in the disclosed methods includethe QDOT nanocrystal products, such as QDOT 525 nanocrystals, QDOT 545nanocrystals, QDOT 565 nanocrystals, QDOT 585 nanocrystals, QDOT 605nanocrystals, QDOT 625 nanocrystals, QDOT 655 nanocrystals, QDOT 705nanocrystals, and QDOT 800 nanocrystals, all available from InvitrogenCorporation (Carlsbad, Calif.).

The lipophilic fluorescent substance can be directly applied to thematerial to be analyzed. Alternatively, the fluorescent substance can bepresent in a liquid solution or suspension. For example, the liquid orsuspension can comprise water and an organic solvent, such as DMSO, DMF,toluene, alcohol (such as methanol, ethanol, or 2-propanol), methylenechloride, and the like, or mixtures thereof.

Methods are provided for identifying a defect in or on coated substrateusing a lipophilic fluorescent substance. A surface of the substrate canbe coated in its entirety, or only a portion of the surface can becoated with a coating. In one method, a hydrophobic polymer substratecoated with a hydrophilic coating, such as alumina, is treated with asolution of a lipophilic fluorescent substance. The fluorescent moleculeor material can selectively bind to defect sites, based on the surfaceadhesion characteristics of the system. The contacting step cangenerally comprise any suitable application method, such as dipping thematerial into a liquid solution or suspension, spraying a liquidsolution or suspension onto the material, spraying the lipophilicfluorescent substance directly onto the material, rolling thefluorescent substance directly onto the material, or combinationsthereof. The lipophilic substance can contact the defect (e.g., crack)and adhere to the underlying polymer substrate left exposed by thedefect. Lipophilic substances are provided that can easily enter intonanometer-scale defects, such as typically found, for example, in ALDbarrier coatings. The lipophilic substance can adhere to the hydrophobicsubstrate via any type of non-covalent interaction (e.g., hydrophobicbonding) by virtue of its hydrophobicity. Further, the lipophilicsubstance has little or no affinity for the hydrophilic surface coatingand can be readily removed from the hydrophilic surface.

The method can further comprise washing the material after thecontacting step and before the detecting step to remove anynon-localized substance. The washing step can be performed once, ormultiple times.

The detecting step can qualitatively detect the presence or absence oflocalized lipophilic fluorescent substance, or can quantitatively detectthe amount of localized lipophilic fluorescent substance. The detectingstep can also determine the location of the localized lipophilicfluorescent substance on the material. The detecting step can compriseapplying radiation to the material in order to detect fluorescenceemitted from the localized lipophilic fluorescent substance. Theparticular type and wavelength of radiation is selected based upon thespectral characteristics of the fluorescent substance, and is wellwithin the talents of the skilled artisan. Examples and sources ofradiation include UV light, lasers, LED light, and visible light. Thedetecting step can further comprise preparing an image of the material.The image can be a film image or an electronic image. Depending on thesize of the defect, a microscope may be useful in detecting andpreparing an image of the defect. The fluorescence emission of thelocalized lipophilic fluorescent substance allows direct identificationand localization of defects. The methods can be used to visualizedefects in many types of materials and can be applied, for example, forthe development and manufacturing of thin film gas diffusion barriersfor the organic light-emitting diodes (OLEDs), photovoltaic (PV), andliquid crystal display (LCD) industries as well as the packaging of:medical devices, sensor skins, electronic circuits, micro-, andnano-systems.

Kits

An additional embodiment of the invention is directed towards kitsuseful for the detection of surface defects in a material. The kits cancomprise at least one lipophilic fluorescent substance (e.g., dyes,fluorescent microspheres, or quantum dots) as described above. The kitscan comprise instructions for performing the above described methods.The kits can comprise a “positive control” material containing at leastone surface defect. The kits can comprise a “negative control” materialthat does not contain surface defects. The kits can comprise a washmaterial useful for removing non-localized fluorescent substance fromthe material.

The following examples are included to demonstrate preferred embodimentsof the invention. It should be appreciated by those of skill in the artthat the techniques disclosed in the examples which follow representtechniques discovered by the inventor(s) to function well in thepractice of the invention, and thus can be considered to constitutepreferred modes for its practice. However, those of skill in the artshould, in light of the present disclosure, appreciate that many changescan be made in the specific embodiments which are disclosed and stillobtain a like or similar result without departing from the scope of theinvention.

EXAMPLES Example 1 Binding of Lipophilic Fluorescent Materials toPolymers

A piece of 2 cm×2 cm sized thin polyethylene terephthalate (PET) plasticfilm coated on one side with alumina. About 3 mm-wide edge on the liftside of the film is not coated. The film was immersed in to a solutionof 1,3-dimethyl-5-styryl BODIPY (Invitrogen Corp., Carlsbad, Calif.;0.04 mg/mL in 70% ethanol, 30% deionized water (v/v) for 3 minutes. Thefilm was removed and washed with 70% ethanol (v/v) three times andexamined with a Nikon fluorescence microscope with a 550 nmexcitation/570 nm emission filter set. The uncoated edge of polymermembrane became red fluorescent; the alumina coating was not stained.

Example 2 Detection of Surface Defects Using Dyes

An equilateral triangle-shaped scratch (about 1 mm×1 mm×1 mm; thescratch lines had a width of about 0.1 mm) was made on a piece ofalumina coated thin polyethylene terephthalate (PET) plastic film tomimic a coating defect. The film was immersed in to a solution of1,3-di-n-propyl BODIPY (Invitrogen Corp., Carlsbad, Calif.; 0.04 mg/mLin 70% ethanol, 30% deionized water) for 2 minutes. The film was removedand washed with 70% (v/v) ethanol three times and examined using a Nikonfluorescence microscope using a standard FITC filter set (490 nmexcitation/515 nm emission). The scratch became green fluorescent basedon the deepness of the damage. The remaining unscratched alumina coatingwas not stained. This result indicated that the defect in a largealumina coated film can be 1) labeled with fluorescent dye, 2) easilydetected and 3) easily located.

Example 3 Detection of Surface Defects Using Fluorescent Microspheres

Several scratches (about 2 mm long and 0.02 mm wide) were made byscratching a piece of alumina-coated thin polyethylene terephthalate(PET) membrane with a sharp 22 gauge syringe needle to mimic a defect.

A suspension of 20 nm green fluorescent microspheres (emission maximumat 515 nm) with low surface charge was prepared by adding 2% microspherestock to a 50% ethanol, 50% deionized water mixture (v/v) for a finalconcentration of 0.5% microsphere.

The membrane sample was immersed into the microsphere suspension for 3minutes at room temperature. The film was removed and washed with 50%ethanol (v/v) three times. The membrane was allowed to dry in air, andwas examined using a Nikon fluorescence microscope with a FITC filterset (excitation: 490 nm/emission: 515 nm). The scratches became brightgreen fluorescent, and were easily visualized and localized on themembrane.

Example 4 Detection of Surface Defects Using Dually FluorescentMicrospheres

Several scratches (about 2 mm long and 0.02 mm wide) were made byscratching a piece of alumina-coated thin polyethylene terephthalate(PET) membrane with a sharp 22 gauge syringe needle to mimic a defect.

A suspension of 110 nm dual emission microspheres (emission max at 565nm and 755 nm) with low surface charge was prepared by adding 5%microsphere stock to a 50% ethanol, 50% deionized water mixture (v/v)for a final concentration of 0.5% microsphere.

The membrane sample was immersed into the microsphere suspension for 3minutes at room temperature. The film was removed and washed with 50%ethanol (v/v) three times. The membrane was allowed to dry in air, andwas examined using a Nikon fluorescence microscope with a XF101 filterset (excitation: 543 nm/emission: 565 nm) and a XF48-2 filter set(excitation: 635±25 nm/emission: 725 nm long pass). The scratches becameorange fluorescent when examined under the XF101 filter, and became redfluorescent when examined under the XF48-2 filter set.

Example 5 Visualization of Mechanical Cracks

Mechanical cracks were visualized using a diaza-indacene fluorophorewith hydrophobic substituents. 25 nm thick ALD alumina barrier filmswere deposited onto polyethylene naphthalate (PEN) substrates (TeonexQ65, Dupont Teijin, Inc.). The coated specimens, some of which weremechanically manipulated in order to intentionally generate defects,were then soaked in a fluorescent tag solution for 5 min. Solventsolution containing 70% ethanol and 30% water was used to wash awayexcess tag molecules not attached to the film. The sample was then driedusing clean dry air and maintained in an ultraviolet-safe environment. ALSM 510 confocal microscope (Carl Zeiss, Inc.) was used for inspectionof the tagged sample. A 488 nm Argon 12 laser source was used to excitethe tags and the fluorescent emission (maximum at 515 nm) was measuredwith a 505-530 nm band pass filter. A PEN substrate with no coating, aPEN substrate with an ALD alumina coating, and an identically coated PENsubstrate bearing intentionally-made scratches were compared. The tagmolecule attached well to the bare PEN film, yielding a bright fieldacross the whole sample, whereas an all dark field image revealed thatthe tag did not attach to the ALD alumina (data not shown). FIG. 1 showsthat the fluorescent molecule selectively attached only to thehydrophobic PEN substrate, where it is exposed by the scratch in thehydrophilic ALD alumina coating.

Example 6 Visualization of Mechanical “Channel Cracks”

The failure mode of “channel cracking” is commonly encountered when abrittle inorganic coating is subjected to mechanical strain or thermalcycling. However, a series of such cracks is not readily observed intransparent films. To demonstrate the use of lipophilic fluorescenttags, an external tensile loading was applied to PEN substrates coatedwith 25 nm of ALD alumina. The fluorescent tags were then applied tothese specimens according the procedure described in Example 5. FIG. 2shows cracks identified across the gage section of a specimen that waselongated to 5% strain. Such cracks, which propagated in the directionorthogonal to the applied load, are common when the stress in brittlefilms exceeds their critical threshold limit. The cracks in FIG. 2A maybe distinguished from those at the edges of the specimen, shown in FIG.2B, which were generated during the sample preparation. Specifically,these edge-located cracks were generated when the alumina ACD coatedspecimen was cut to size prior to testing. FIG. 2B identifies the uniquecharacteristics of the shear cracks, which quickly arrest near the edgeof the specimen. Excellent image contrast was obtained in all of theconfocal measurements, allowing cracks to be readily identified despiteminimal sample preparation. Field emission scanning electron microscopy(FESEM) was used to measure the width of the cracks. At the fully formedregion of the shear cracks, the crack width of about 20 nm was observedusing a JSM-7401F field emission scanning electron microscope (JEOLLimited), FIG. 2C.

Example 7 Visualization of Individual Defects and Particles

In contrast to mechanical cracks, individual defects or pinholes aregenerally caused by particulate contamination and/or the substratesurface roughness. Tiny individual defects in submicron/nanoscale sizeare the critical features limiting barrier performance. These defectshave to be inspected and controlled to assure the barrier quality andhigh yield barrier manufacturing. ALD alumina barrier films weredeposited onto PEN substrates and treated with fluorescent tags, asdescribed in Example 5. FIG. 3A is an image collected using a confocalmicroscope with a 20× objective showing a defect rich region in the 25nm thick Al₂O₃ ALD film. White arrows in FIG. 3A indicate prescribedmarker features, used to facilitate defect location for further FESEMimaging. To verify the individual defects and determine the defect size,sites #1 and #2, shown in FIGS. 3B and 3C, respectively, weresubsequently observed using FESEM. Diameters of ˜200 nm and ˜1.2 μm weredetermined for sites #1 and #2, as indicated in FIGS. 3B and 3C.However, defects smaller than 200 nm also were rendered visible bytreatment with the fluorescent tag molecule. The images demonstrate thatdefect sizes between tens and hundreds of nanometers can be readilyvisualized after treatment with the lipophilic fluorescent tagsubstance. FIG. 3 also provides information about the morphology of theindividual defects. From FIG. 3B, the oval shaped defect bears a tinycrack at its top end. The defect in FIG. 3C shows a region where theAl₂O₃ ALD film was not able to bind to the polymer surface, likely theresult of particle contamination. Although the identified defectspossibly could be observed using SEM, defect inspection becomes verycumbersome because the defect location as well as the defect densitycannot be determined at low magnification. Further, examination at highmagnification with small field size is very time-consuming. Comparedwith SEM and AFM observation, visualization of lipophilic, fluorescentsubstances according to the present method allows examination of a largefield size and offers the advantage of continuous inspection at lowmagnification.

All of the compositions and/or methods disclosed and claimed herein canbe made and executed without undue experimentation in light of thepresent disclosure. While the compositions and methods of this inventionhave been described in terms of preferred embodiments, it will beapparent to those of skill in the art that variations may be applied tothe compositions and/or methods and in the steps or in the sequence ofsteps of the methods described herein without departing from the conceptand scope of the invention. More specifically, it will be apparent thatcertain agents which are chemically related may be substituted for theagents described herein while the same or similar results would beachieved. All such similar substitutes and modifications apparent tothose skilled in the art are deemed to be within the scope and conceptof the invention.

All of the U.S. patents, U.S. patent application publications, U.S.patent applications, foreign patents, foreign patent applications andnon-patent publications referred to in this specification areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

1. A method of identifying a defect in a surface, comprising: a)providing a substrate having a hydrophobic surface at least partiallycoated by a hydrophilic layer, wherein the hydrophilic layer has thedefect therein; b) contacting the substrate with a lipophilic,fluorescent substance, for a sufficient amount of time for the substanceto contact the defect; c) exciting the fluorescent substance with energyat an appropriate wavelength to generate a detectable fluorescenceresponse; and, d) detecting the fluorescence response of the substance.2. The method of claim 1, further comprising washing the substrate aftercontacting the substrate with the lipophilic, fluorescent substance. 3.The method of claim 1 wherein the substrate comprises a polymer.
 4. Themethod of claim 1 wherein the hydrophilic layer is or comprises aninorganic material.
 5. The method of claim 1 wherein the lipophilic,fluorescent substance is a fluorescent compound that comprises a4,4-difluoro-4-bora-3a,4a-diaza-s-indacene moiety.
 6. The method ofclaim 1 wherein the lipophilic, fluorescent substance further comprisesa lipophilic moiety.
 7. The method of claim 6 wherein the lipophilic,fluorescent substance further comprises two or more lipophilic moieties.8. The method of claim 6 wherein the lipophilic moiety is a hydrocarbonhaving 1-20 carbon atoms.
 9. The method of claim 6 wherein thelipophilic moiety is an alkyl group having 1-20 carbon atoms.
 10. Themethod of claim 6 wherein the lipophilic moiety is phenyl or styrylgroup.
 11. The method of claim 1 wherein the hydrophilic layer is lessthan 10 Å in thickness.
 12. The method of claim 1 wherein thelipophilic, fluorescent substance is associated with a microparticle.13. The method of claim 1 wherein the lipophilic, fluorescent substanceis a semiconductor nanocrystal.
 14. A lipophilic, fluorescent substancethat comprises a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene moiety and alipophilic moiety.
 15. The lipophilic, fluorescent substance of claim 14wherein the lipophilic moiety is a hydrocarbon having 1-20 carbon atoms.16. The lipophilic, fluorescent substance of claim 14 wherein thelipophilic moiety is an alkyl group having 1-20 carbon atoms.
 17. Thelipophilic, fluorescent substance of claim 14 wherein the lipophilicmoiety is a phenyl or styryl group.
 18. The lipophilic, fluorescentsubstance of claim 14 wherein the substance is associated with amicroparticle.
 19. A substrate comprising an identifiable defect: a) ahydrophobic surface, a substrate having a hydrophobic surface at leastpartially coated by a hydrophilic layer, wherein the hydrophilic layerhas the defect therein; and b. a lipophilic, fluorescent substance thatis in contact with the defect.
 20. The substrate of claim 19 wherein thelipophilic, fluorescent substance comprises a4,4-difluoro-4-bora-3a,4a-diaza-s-indacene moiety and a lipophilicmoiety.